AF Commercial Driving Theory key terms

The maximum legal speed allowed on a given road or in a given area, shown by signs or set by default rules, applying to all vehicles unless a lower limit is posted.

The priority a road user has to proceed first at a junction, crossing or narrowing, determined by signs, markings, signals or general rules rather than by assertiveness.

A section of road passing through a town or village, usually marked by place-name signs, where lower default speed limits and stricter parking rules normally apply.

A rule or sign that forbids passing another moving vehicle at a particular place or for a particular class of vehicle, often because visibility or road width is insufficient.

The total distance a vehicle travels from the moment a hazard is noticed until it comes to rest, made up of thinking distance plus braking distance.

A simple following-distance guide in good conditions: after the vehicle ahead passes a fixed point, at least two seconds should elapse before you reach it.

A broken or solid line across the carriageway, often paired with a triangle marking, showing where a driver must stop or yield to traffic on the priority road.

A solid white line across the lane at a junction, traffic light or railway crossing that marks the point beyond which a vehicle must not proceed while required to stop.

A continuous centre or edge line that generally may not be crossed, used where overtaking or lane changes would be dangerous because of limited visibility.

A dashed centre or lane line that may be crossed when it is safe and legal to do so, for example to overtake or change lanes.

The fixed order in which vehicle signals change, typically green, amber, red and back to green, where amber warns that the signal is about to turn red.

An additional illuminated arrow on a traffic signal permitting movement only in the direction shown, while other movements remain controlled by the main signal.

A circular junction where traffic already on the circle normally has priority and entering drivers yield, with lane choice depending on the intended exit.

A sign, usually circular, that imposes an obligation such as a direction to follow, a minimum speed or a requirement to use a particular route.

A sign, usually circular with a red border, that forbids a stated action such as entry, parking, turning or exceeding a stated weight or speed.

A sign, usually triangular with a red border, that alerts drivers in advance to a hazard such as a bend, junction, steep hill or crossing.

The maximum vehicle height permitted to pass a bridge, tunnel or barrier, shown by a sign or gauge board and compared against the vehicle's actual overall height.

The maximum permitted total weight of a vehicle together with its load, fuel and occupants, as specified by the manufacturer and by the applicable legal limit.

The portion of a vehicle's total weight carried by a single axle or axle group, which must stay within legal and manufacturer limits to avoid damage and instability.

The weight of goods, passengers and other contents a vehicle may carry, found by subtracting the vehicle's unladen weight from its permitted maximum gross weight.

The way weight is spread across a vehicle's axles and floor, which affects steering, braking, stability and legal axle loads and must be planned before loading.

The use of straps, chains, bars or sheeting to stop a load from sliding, tipping, rolling or falling off during normal driving, braking and cornering.

The maximum force a strap, chain or other securing device is rated to withstand in normal service, used to match the restraint to the weight and type of load.

The distance a vehicle or its load projects beyond the front or rear of the body, which is legally limited and affects turning clearance and lighting requirements.

A marker board, flag or light required to make a load that extends beyond the vehicle's outline visible to other road users, especially in poor light.

A recording device fitted to certain goods and passenger vehicles that logs driving time, other work, breaks and rest, and must be used correctly and retained for inspection.

The maximum time a driver may spend driving within a single day, normally nine hours, extendable to ten hours a limited number of times per week.

The minimum uninterrupted period within each 24-hour cycle during which a driver must be free from all work, normally at least eleven hours and reduced only within permitted limits.

The longer rest period a driver must take in each weekly cycle, normally at least 45 consecutive hours, which may be reduced under conditions that must be compensated.

The rule requiring a driver to take a minimum uninterrupted break after a set period of driving, intended to reduce fatigue and maintain attention.

The physical and mental tiredness that slows reactions and impairs judgement, managed by planning journeys, taking breaks and not driving when drowsy.

A personalised smart card inserted into a digital tachograph that identifies the driver and stores their activity records, which must be carried and produced on request.

The routine inspection of tyres, lights, brakes, mirrors, couplings and fluids before a journey, with any fault affecting safety reported and rectified before driving.

A short physical check around the vehicle before departure to confirm the load is secure, lights work, nothing is trapped and no leaks or damage are visible.

The minimum legal depth of tread remaining across the tyre's central band, below which the tyre must be replaced because grip and water clearance are inadequate.

Loss of tyre contact with the road because a film of water lifts the tyre, causing a sudden loss of steering and braking, most likely at speed in heavy rain.

An area around the vehicle that cannot be seen in the mirrors, requiring a direct check before changing lane or turning to avoid striking a road user beside you.

Following another vehicle too closely, which removes the time and space needed to stop if it brakes suddenly and is a common cause of rear-end collisions.

A loss of control in an articulated vehicle where the tractor and trailer fold against each other, often triggered by harsh braking or steering on a slippery surface.

A loss of tyre grip causing the vehicle to slide, corrected by easing off the accelerator or brake, steering smoothly and avoiding sudden inputs.

A further impact after an initial incident, for example a following vehicle hitting the stopped casualty or debris, prevented by warning triangles, lights and safe positioning.

The steps taken after a collision to make the area safe, including hazard lights, warning devices, high-visibility clothing and keeping traffic clear of casualties.

A reflective folding triangle placed on the road behind a broken-down or damaged vehicle to warn approaching traffic, at a distance suited to the road and visibility.

The sequence used at a casualty scene: check for danger, assess responsiveness and breathing, call emergency services, then treat severe bleeding and shock.

A stable side-lying posture used for an unconscious casualty who is breathing, helping keep the airway open and allowing fluids to drain.

A qualification card proving the holder has completed the required periodic training for professional drivers, which must be carried and shown during roadside checks.

The authorisation required to operate goods vehicles for hire or reward, setting conditions on maintenance, vehicle numbers and the repute of the operator.

A document confirming that at least the minimum compulsory third-party cover is in force for the vehicle, which must be held and produced when requested.

The official record of a vehicle's registered keeper, identifying details and technical data, which should be kept accurate and available for inspection.